Slate is making its coronavirus coverage free for all readers. Subscribe to support our journalism. Start your free trial.

Of all the great number of things that we want right now and cannot have, I’d wager that perhaps the tip top of the list is: information. There is an enormous gap between what we want to know about the coronavirus—how long will it last, how do we best treat it, how do we avoid getting it, what do we do if we start to feel sick, when do you know to go to the hospital—and what we actually know. That lack of information, coupled with a big dollop of fear, makes anything that seems to tell you how to survive the virus extremely tantalizing.

On Monday, the New York Times published an opinion piece from a lung specialist about what makes the virus so dangerous and what could be done to make it less so. Its author, Richard Levitan, left the relative safety of New Hampshire to spend 10 days treating patients at the epicenter of the outbreak in New York City and learning what he could about fighting the virus. During that time, his lung-expert brain noticed something odd: Many of the patients who had serious cases did not seem as visibly distressed as doctors would expect, even as their lungs were being compromised and their oxygen levels decimated.

As Levitan writes:

A vast majority of Covid pneumonia patients I met had remarkably low oxygen saturations at triage—seemingly incompatible with life—but they were using their cellphones as we put them on monitors. Although breathing fast, they had relatively minimal apparent distress, despite dangerously low oxygen levels and terrible pneumonia on chest X-rays.

Levitan’s piece outlines the scary consequences of the body being low on oxygen but not feeling like it is low on oxygen. He writes that because these patients often feel relatively OK, they aren’t getting treated soon enough. As a result, their lungs experience greater damage, and patients require more invasive and intensive care, often paired with lower likelihood of survival. This is a scary thing to learn during a pandemic in which the common wisdom has become that anyone who can should stay home for as long as they are able, so as to not overwhelm hospitals. Luckily, Levitan also has a potential remedy to this problem:

There is a way we could identify more patients who have Covid pneumonia sooner and treat them more effectively—and it would not require waiting for a coronavirus test at a hospital or doctor’s office. It requires detecting silent hypoxia early through a common medical device that can be purchased without a prescription at most pharmacies: a pulse oximeter.

A pulse oximeter is a little device that, when clipped to your finger, can give you a read out of your oxygen level. (For most healthy people, oxygen levels are between 94 and 100 percent when awake, with doctors getting concerned when they drop below 90 percent. Levitan writes that in his NYC hospital, he treated COVID patients with oxygen levels as low as 50 percent.) Perhaps pulse oximeters were available for purchase without a prescription at most pharmacies when Levitan was drafting his piece. But since its publication, they’ve become mighty hard to find—they were sold out at mostpharmacies when I checked on Tuesday afternoon, and on Amazon, the ones that are actually well-reviewed were sold out, too. (The ones that are not well-reviewed are likely not approved by the Food and Drug Administration and, according to this study, are not worth your time.)

Getting the word out about how useful these devices might be means that for now, they have disappeared from most people’sgrasp.

Levitan’s piece was not the first time pulse oximeters have been brought up as being useful for people dealing with COVID-19. Jessica Lustig, a deputy editor at the New York Times Magazine, mentioned the device in her viral March essay about nursing her husband through the illness at home. (Hers was “brought by a friend from the drugstore on the doctor’s advice.”) After recovering from COVID-19, Bravo’s Andy Cohen also recommended them in March, as an essential tool for anyone worried about the virus. And as Quartz reported in early April, interest in oximeters has been high ever since the first case of the coronavirus was reported in the U.S. way back in January—demand spiked by more than 500 percent that week.

But Levitan’s piece is more direct about their utility. He concludes by arguing that everyone who has a cough and fever—whether they’ve tested positive, negative, or not at all—should monitor themselves with these devices for two weeks. The recommendation has added allure by virtue of coming from a doctor and, even more than that, from a lung expert. It feels almost nuts, after finishing the piece, not to think about procuring a pulse oximeter as quickly as possible—he makes it sound like these tools might be a short cut in helping us figure out a better way to triage our overwhelmed hospitals. And yet, in a cruel twist, Levitan getting the word out about how useful these devices might be means that for now, they have disappeared from most people’s grasp.

As someone who has not yet purchased a pulse oximeter myself, I was curious about how hard I should work to try to acquire one. I was also curious about what the rush on them might mean. Is this another N95 mask situation, where the public wising up to the supposed utility of something ends up shuffling them away from the people who need them most? I emailed Levitan to ask, and his reply was reassuring: “There’s no competition between hospitals and home devices; we use different ones that are a lot more expensive, plug into cardiac monitors, etc.,” he wrote me. His further comments make clear that his advice is a long-term suggestion, not an immediate one:

This pandemic is likely not going away this winter … maybe something we are battling for several years—pulse oximeters should be like a thermometer in your house; valuable information you contact your physician about to make a decision about need for evaluation and treatment.

This makes sense to me. In Levitan’s Times piece, he doesn’t purport to offer specific advice on what to do with the information your oximeter tells you—there’s no percentage reading he offers as the number at which you should register your alarm, or decide to call your doctor when you otherwise wouldn’t have. That’s because doctors still need to figure that out. Which means that even if you have COVID-19 and a pulse oximeter, you’ll still need to talk to your doctor about how to use it. In other words, it’s still the doctor, not the pulse oximeter, that’s going to get you through this.

I also asked Jeremy Faust, an emergency doctor and Slate contributor, what he thought of the piece and the run on pulse oximeters. He said:

All medical devices provide information that is not so easy to interpret. I see this every time someone in my family wants me to look at the results of their routine blood work. They see all of these “alert” and abnormal values, and they’re worried. But they’re mostly meaningless. The same can be said about devices that measure our physiology. For every questionable story of some smartwatch catching some abnormal heart rhythm, there are untold numbers of false alarms, leading to unnecessary doctor’s office and ER visits.

Pulse oximeters might be a great tool for COVID-19. But only if you’ve been diagnosed, or really think you have it. Even then, a low oxygen reading might be meaningful or meaningless.

In other words, like so much else, the possible role of pulse oximeters is still unclear—including how exactly doctors can use them to better serve patients, and then how doctors can help individuals at home use them. Which means—if you have a pulse oximeter, great. If you don’t right now, that’s also fine—calling your doctor if you’re sick will still be your first line of defense. It seems likely that over the next few years, they’ll become household items. But that doesn’t mean it’s the essential tool that will ensure you get through this. It just means that like everything else, we’re still figuring it out.